[Study of transcranial magnetic stimulation on diaphragm in patients with obstructive sleep apnea-hypopnea syndrome]

To investigate the changes and possible mechanisms of diaphragm motor evoked potential (MEP) elicited by transcranial magnetic stimulation (TMS) in patients with obstructive sleep apnea-hypopnea syndrome (OSAHS).

Sixteen healthy volunteers (control group), 7 primary snorers (snore group), 13 mild-moderate OSAHS patients (mild-moderate group) and 16 severe OSAHS patients (severe group) were recruited for the study from June in 2005 to June in 2006. Esophageal electrodes combined with TMS and cervical magnetic stimulation (CMS) were used to measure the latency and amplitude of right diaphragm MEP, as well as central motor conduction time (CMCT). The study was repeated in 5 OSAHS patients after effective nasal continuous positive airway pressure (nCPAP) treatment for at least 2 months.

The amplitude of right MEP in severe OSAHS group was (152 +/- 116) microV, which was significantly lower than that in the control group (414 +/- 201) microV, the snore group (352 +/- 99) microV and the mild-moderate group (372 +/- 206) microV. The latency and CMCT in the severe OSAHS group were (18.1 +/- 1.8), (10.6 +/- 1.8) ms respectively, which were significantly longer than those in the control group (13.9 +/- 1.6), (7.7 +/- 1.7) ms, the snore group (14.6 +/- 1.6), (8.1 +/- 1.6) ms, and the mild-moderate group (15.4 +/- 2.7) , (9.0 +/- 2.2) ms. The latency and amplitude of diaphragm MEP as well as CMCT correlated significantly with arousal index, longest apnea duration, minimum pulse oxygen saturation (SpO2), oxygen desaturation index, the percentage of total sleep time with SpO2 below 90% and apnea-hypoxia index (AHI). The latency became significantly shorter after effective nCPAP treatment for more than 2 months, which was (17.5 +/- 0.6) and (15.5 +/- 0.7) ms respectively.

The latency of MEP and CMCT in OSAHS patients prolonged significantly, while the amplitude of MEP lowered, which may be due to repeated hypoxia, carbon dioxide retention and disorder of sleep structure at night.